The long-term goal of this research is to understand the neural mechanisms underlying simple forms of visually based cognition, including visually based decision-making in particular. The projects will focus on a network of high-level brain structures that appears to translate perception of the visual world into plans for action. Prior studies indicate that this network includes cortical areas of the parietal and frontal lobes as well as midbrain structures such as the superior colliculus. A similar network of structures is present in humans, and the proposed research is thus likely to contribute directly to our developing knowledge of human vision, cognition, and their clinical disorders. Three specific aims will be pursued during the coming grant period: 1. Electrical microstimulation techniques will be employed to test rigorously the causal role played by each candidate neural structure in visually-based decision making. 2. Combined stimulation and recording techniques will be employed to test specific hypotheses concerning the functional circuitry that connects these areas and the infromation that flows between them. 3. Electrophysiological techniques will be employed to study identify and study the neural mechanisms that compute the "subjective value" that an organism places on alternative actions. Psychological and economic studies have shown that perceived value exerts an enormous influence on decisionmaking. Together the proposed experiments will provide considerable impetus toward understanding the neural mechanisms underlying a simple form of cognition. The ultimate health-related value of this work will follow from an understanding of the biological basis of mental function. Neurological and psychiatric diseases that affect mental function take a massive toll on the health and well-being of our citizenry. These diseases are particularly insidious because they slowly rob the afflicted person of normal cognitive abilities - the very essence of personal identity. Understanding how brain activity gives rise to mental function in normal subjects will undoubtedly provide a deeper understanding of what goes wrong in various disease processes, and suggest useful therapeutic approaches for such diseases.